Android 使用非阻塞的方式读写串口

正常Android设备的串口一般是用作debug调试使用，随着Android设备使用越来越广，比如智能pos、智能扫码机都会用到Android主板和单片机进行通信，如果Android主板和单片机通信数据量大可以使用USB，若是通信数据量小可以使用串口进行通信，因为串口通信简单并且稳定性高，最近做的一个项目就是Android使用串口和加密芯片进行通信，Android主板使用的是rk3288和rk3368. 在rk3288源码中集成了一个串口demo，目录在

rk3288/frameworks/base/tests/SerialChat
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网上存在一个demo是通过 java->jni->Serial驱动，虽然也可以正常读写，这样做缺点是
1、如果突然串口不能正常通信可能会导致app崩溃，
2、这个串口只能被当前的app使用，其他app 不能使用。
3、违背正常Android设计初衷，Android标准流程是
java->service->jni->hal->serial驱动。
所以我在项目中使用了Android源码中的demo

public class SerialChat extends Activity implements Runnable, TextView.OnEditorActionListener {

private static final String TAG = "SerialChat";

private TextView mLog;
private EditText mEditText;
private ByteBuffer mInputBuffer;
private ByteBuffer mOutputBuffer;
private SerialManager mSerialManager;
private SerialPort mSerialPort;
private boolean mPermissionRequestPending;

private static final int MESSAGE_LOG = 1;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

mSerialManager = (SerialManager)getSystemService(Context.SERIAL_SERVICE);
setContentView(R.layout.serial_chat);
mLog = (TextView)findViewById(R.id.log);
mEditText = (EditText)findViewById(R.id.message);
mEditText.setOnEditorActionListener(this);

if (false) {
mInputBuffer = ByteBuffer.allocateDirect(1024);
mOutputBuffer = ByteBuffer.allocateDirect(1024);
} else {
mInputBuffer = ByteBuffer.allocate(1024);
mOutputBuffer = ByteBuffer.allocate(1024);
}
}

@Override
public void onResume() {
super.onResume();

String[] ports = mSerialManager.getSerialPorts();
for(int 1 = 0;i < ports.length;i++ ){
Log.e("PPTV", "ports is ====" + ports[i] );
}
if (ports != null && ports.length > 0) {
try {
mSerialPort = mSerialManager.openSerialPort(ports[1], 115200);
if (mSerialPort != null) {
new Thread(this).start();
}
} catch (IOException e) {
}
}

}

@Override
public void onPause() {
super.onPause();

}

@Override
public void onDestroy() {
if (mSerialPort != null) {
try {
mSerialPort.close();
} catch (IOException e) {
}
mSerialPort = null;
}
super.onDestroy();
}

public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
if (/* actionId == EditorInfo.IME_ACTION_DONE && */ mSerialPort != null) {
try {
String text = v.getText().toString();
Log.d(TAG, "write: " + text);
byte[] bytes = text.getBytes();
mOutputBuffer.clear();
mOutputBuffer.put(bytes);
mSerialPort.write(mOutputBuffer, bytes.length);
} catch (IOException e) {
Log.e(TAG, "write failed", e);
}
v.setText("");
return true;
}
Log.d(TAG, "onEditorAction " + actionId + " event: " + event);
return false;
}

public void run() {
Log.d(TAG, "run");
int ret = 0;
byte[] buffer = new byte[1024];
while (ret >= 0) {
try {
Log.d(TAG, "calling read");
mInputBuffer.clear();
ret = mSerialPort.read(mInputBuffer);
Log.d(TAG, "read returned " + ret);
mInputBuffer.get(buffer, 0, ret);
} catch (IOException e) {
Log.e(TAG, "read failed", e);
break;
}

if (ret > 0) {
Message m = Message.obtain(mHandler, MESSAGE_LOG);
String text = new String(buffer, 0, ret);
Log.d(TAG, "chat: " + text);
m.obj = text;
mHandler.sendMessage(m);
}
}
Log.d(TAG, "thread out");
}

Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_LOG:
mLog.setText(mLog.getText() + (String)msg.obj);
break;
}
}
};
}

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首先是获取串口服务

mSerialManager = (SerialManager)getSystemService(Context.SERIAL_SERVICE);
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如果要想通过getSystemService获取serial服务，首先要在
core/java/android/content/Context.java:
添加

public static final String SERIAL_SERVICE = "serial";
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在ContextImpl.java 中注册服务

registerService(SERIAL_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
IBinder b = ServiceManager.getService(SERIAL_SERVICE);
return new SerialManager(ctx, ISerialManager.Stub.asInterface(b));
}});
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每次开机会自动启动。可以通过命令查看当前服务是否启动

adb shell service list
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可以看到服务已经启动。
目前启动的服务Java层面的服务，只是对我们C语言串口服务做了一层封装，真正工作的是我们native serial(SerialService).
所以registerService 函数中会获取SerialService的代理端，

IBinder b = ServiceManager.getService(SERIAL_SERVICE);
return new SerialManager(ctx, ISerialManager.Stub.asInterface(b));
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SerialService 注册在SystemServer.java 中

try {
Slog.i(TAG, "Serial Service");
// Serial port support
serial = new SerialService(context);
ServiceManager.addService(Context.SERIAL_SERVICE, serial);
} catch (Throwable e) {
Slog.e(TAG, "Failure starting SerialService", e);
}
}
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SerialService.java 源码

public class SerialService extends ISerialManager.Stub {

private final Context mContext;
private final String[] mSerialPorts;

public SerialService(Context context) {
mContext = context;
mSerialPorts = context.getResources().getStringArray(
com.android.internal.R.array.config_serialPorts);
}

public String[] getSerialPorts() {
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.SERIAL_PORT, null);

ArrayList ports = new ArrayList();
for (int i = 0; i < mSerialPorts.length; i++) {
String path = mSerialPorts[i];
if (new File(path).exists()) {
ports.add(path);
}
}
String[] result = new String[ports.size()];
ports.toArray(result);
return result;
}

public ParcelFileDescriptor openSerialPort(String path) {
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.SERIAL_PORT, null);
for (int i = 0; i < mSerialPorts.length; i++) {
if (mSerialPorts[i].equals(path)) {
return native_open(path);
}
}
throw new IllegalArgumentException("Invalid serial port " + path);
}

private native ParcelFileDescriptor native_open(String path);
}
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mContext = context;
mSerialPorts = context.getResources().getStringArray(
com.android.internal.R.array.config_serialPorts);
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会获取目前存在可以使用串口列表。这个根据自己需要添加。
我的就使用一个串口3

"/dev/ttyS3"

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回到SerialChat.java

String[] ports = mSerialManager.getSerialPorts();
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结果就是/dev/ttyS3

mSerialPort = mSerialManager.openSerialPort(ports[1], 115200);
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打开串口3

public SerialPort openSerialPort(String name, int speed) throws IOException {
try {
ParcelFileDescriptor pfd = mService.openSerialPort(name);//打开串口
if (pfd != null) {
SerialPort port = new SerialPort(name);
port.open(pfd, speed);//设置波特率及其他属性
return port;
} else {
throw new IOException("Could not open serial port " + name);
}
} catch (RemoteException e) {
Log.e(TAG, "exception in UsbManager.openDevice", e);
}
return null;
}
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结果会调用SerialService.openSerialPort(name)

static jobject android_server_SerialService_open(JNIEnv *env, jobject thiz, jstring path)
{
const char *pathStr = env->GetStringUTFChars(path, NULL);

int fd = open(pathStr, O_RDWR | O_NOCTTY);
if (fd < 0) {
ALOGE("could not open %s", pathStr);
env->ReleaseStringUTFChars(path, pathStr);
return NULL;
}
env->ReleaseStringUTFChars(path, pathStr);

jobject fileDescriptor = jniCreateFileDescriptor(env, fd);
if (fileDescriptor == NULL) {
return NULL;
}
return env->NewObject(gParcelFileDescriptorOffsets.mClass,
gParcelFileDescriptorOffsets.mConstructor, fileDescriptor);
}

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阻塞的方式打开串口

设置串口波特率已经属性

android_hardware_SerialPort.cpp

static void
android_hardware_SerialPort_open(JNIEnv *env, jobject thiz, jobject fileDescriptor, jint speed)
{
switch (speed) {
case 50:
speed = B50;
break;
case 75:
speed = B75;
break;
case 110:
speed = B110;
break;
case 134:
speed = B134;
break;
case 150:
speed = B150;
break;
case 200:
speed = B200;
break;
case 300:
speed = B300;
break;
case 600:
speed = B600;
break;
case 1200:
speed = B1200;
break;
case 1800:
speed = B1800;
break;
case 2400:
speed = B2400;
break;
case 4800:
speed = B4800;
break;
case 9600:
speed = B9600;
break;
case 19200:
speed = B19200;
break;
case 38400:
speed = B38400;
break;
case 57600:
speed = B57600;
break;
case 115200:
speed = B115200;
break;
case 230400:
speed = B230400;
break;
case 460800:
speed = B460800;
break;
case 500000:
speed = B500000;
break;
case 576000:
speed = B576000;
break;
case 921600:
speed = B921600;
break;
case 1000000:
speed = B1000000;
break;
case 1152000:
speed = B1152000;
break;
case 1500000:
speed = B1500000;
break;
case 2000000:
speed = B2000000;
break;
case 2500000:
speed = B2500000;
break;
case 3000000:
speed = B3000000;
break;
case 3500000:
speed = B3500000;
break;
case 4000000:
speed = B4000000;
break;
default:
jniThrowException(env, "java/lang/IllegalArgumentException",
"Unsupported serial port speed");
return;
}

int fd = jniGetFDFromFileDescriptor(env, fileDescriptor);
// duplicate the file descriptor, since ParcelFileDescriptor will eventually close its copy
fd = dup(fd);
if (fd < 0) {
jniThrowException(env, "java/io/IOException", "Could not open serial port");
return;
}
env->SetIntField(thiz, field_context, fd);

struct termios tio;
if (tcgetattr(fd, &tio))
memset(&tio, 0, sizeof(tio));

tio.c_cflag = speed | CS8 | CLOCAL | CREAD;
// Disable output processing, including messing with end-of-line characters.
tio.c_oflag &= ~OPOST;
tio.c_iflag = IGNPAR;// 忽略奇偶校验错误
tio.c_lflag = 0; /* turn of CANON, ECHO*, etc */
/* no timeout but request at least one character per read */
tio.c_cc[VTIME] = 0;//如果读取不到就一直等待
tio.c_cc[VMIN] = 1;//读取一个byte就返回
tcsetattr(fd, TCSANOW, &tio);
tcflush(fd, TCIOFLUSH);
}

Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_LOG:
mLog.setText(mLog.getText() + (String)msg.obj);
break;
}
}
};
}
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开启一个thread方式read 串口数据，
无数据会一直阻塞在ret = mSerialPort.read(mInputBuffer);
另外注意的是读写buffer 要是用

private ByteBuffer mInputBuffer;
private ByteBuffer mOutputBuffer;
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收到数据可以保存到普通的 byte[]中。

public int read(ByteBuffer buffer) throws IOException {
if (buffer.isDirect()) {
return native_read_direct(buffer, buffer.remaining());
} else if (buffer.hasArray()) {
return native_read_array(buffer.array(), buffer.remaining());
} else {
throw new IllegalArgumentException("buffer is not direct and has no array");
}
}
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调用底层的c语言的read函数

static jint
android_hardware_SerialPort_read_direct(JNIEnv *env, jobject thiz, jobject buffer, jint length)
{
int fd = env->GetIntField(thiz, field_context);

jbyte* buf = (jbyte *)env->GetDirectBufferAddress(buffer);
if (!buf) {
jniThrowException(env, "java/lang/IllegalArgumentException", "ByteBuffer not direct");
return -1;
}

int ret = read(fd, buf, length);
if (ret < 0)
jniThrowException(env, "java/io/IOException", NULL);
return ret;
}
---------------------
版权声明：本文为CSDN博主「九霄的爸爸」的原创文章，遵循CC 4.0 by-sa版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/lb5761311/article/details/80618834

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